The invention relates to an inductor core for an inductively heatable godet roll as well as an inductor and an inductively heatable godet roll. The inductor core comprises a plurality of inductor core laminations arranged radially in a star shape with radial sections and respectively one outer and one inner axial section. In the inductor a sleeve is arranged around the inductor core laminations, wherein the outer axial sections of the inductor core laminations are adjacent to the sleeve. These godet rolls are used in spinning machines or on machines for manufacturing fibres, e.g. yarns, as guide rollers and take-off rolls for the fibres to be processed.
Inductively heatable godet rolls are known in the prior art. These godet rolls have a magnetic inductor core which is wound with coil windings wherein the coil windings are acted upon by an electrical alternating current. The coil windings together with the inductor core form an inductor which makes it possible to inductively heat the godet roll. The inductor core thereby brings about a focussing and amplification of the magnetic field generated by the coil windings through which current flows. The magnetic field induced by the inductor induces electrical eddy currents in the electrically conducting parts of the godet roll which heat the electrically conducting parts and therefore the godet roll.
Inductor cores of cast iron are known. Inductor cores of cast iron can be manufactured cheaply but at low magnetic field strengths, i.e., at around 1100 VA, the inductor cores reach magnetic saturation which makes it difficult for the magnetic field generated by the electric current flowing in the coil windings to penetrate into the inductor core. Thus, high heating powers which make it possible to heat the surfaces of the godet roll coming in contact with the fibres to be processed to a temperature of 240° or higher required in various fibre processing methods, are difficult to achieve using cast-iron inductor cores. In addition, electrical eddy currents are also induced in these inductor cores. This results in heating of the inductor core itself which makes it difficult to quickly control the godet roll temperature.
Temperatures of 240° C. can be achieved when the power consumption of the godet roll is 1100 VA but only at low rotation speeds of the godet roll. Most power is used to compensate for the heat losses to the environment of the rapidly rotating godet roll. As the rotation speed increases, this heat loss increases quadratically. 1100 VA is a power limit for a godet roll having an overall size of 90 mm length and 100 mm diameter. Larger godet rolls allow higher heating powers with a cast-iron inductor core. However, an increase in the size of the godet roll results in a larger surface of the godet roll whereby the loss of heat energy proportional to this surface increases. A large fraction of the heating power obtained by increasing the size of the godet roll is thereby compensated.
Inductors with laminated inductor cores are further known. In these inductor cores, inductor core laminations arranged radially spaced apart in a star shape, having radial sections and respectively one outer and one inner axial section are arranged around an inner tube such that the inductor core laminations have their inner axial section respectively adjacent to the outer surface of the inner tube. In this case, the inductor core laminations are welded with their inner axial section respectively on the outer surface of the inner tube. The inductor core laminations are made of transformer sheet metal. The inductor core is wound with coil windings. During winding care must be taken to ensure that any insulation of the wire used to construct the coil windings is not damaged. Laminated inductor cores prevent the formation of eddy currents in the inductor core in accordance with a laminated transformer core. If the sleeve is made of an electrically conductive material, e.g. of steel, eddy currents are induced in the sleeve, resulting in heating of the sleeve and thus of the godet roll into which the inductor is inserted. The inductor core itself is not significantly heated by the lamination of the inductor core. Local heating near the surface of the godet roll is achieved. As a result of the material used to manufacture the laminations, laminated inductor cores have significantly higher magnetic saturation limits than cast-iron inductor cores whereby substantially higher magnetic fields can be generated by means of the inductors. A disadvantage with known laminated inductor cores is that the inductor core laminations must be welded individually to the inner tube. Further, it is expensive to arrange the inductor core laminations in a star shape i.e., spaced apart at the outer diameter. For this purpose, the metal sheets from which the inductor core laminations are made, are provided with a lug as a spacer at their outer regions. During assembly of the inductor core the metal sheets are then arranged individually. For better fixing the sheets can be fixed to a sleeve using a welded seam whereby disadvantageous eddy currents are produced during operation of a godet roll fitted with an inductor core of this type.
High heating powers can certainly be achieved with laminated inductor cores but they are expensive to manufacture and therefore cost-intensive.
The documents DE 19 57 110 A1 and CH 467 363 A each disclose a heatable godet roll with an inductor core comprising a plurality of inductor core laminations arranged radially in a star shape, wherein fixing means are provided as locating means. The locating means are formed circumferentially on end plates to prevent the inductor core laminations from slipping in a radial direction.
Document U.S. Pat. No. 3,448,233 discloses a heatable godet roll with an inductor core which comprises a plurality of inductor core laminations arranged radially in a star shape and being formed from rectangular packages of sheet metal.
It is the object of the invention to provide an inductor core and an inductor for an inductively heated godet roll and an inductively heatable godet roll which avoid the disadvantages of the prior art and especially are simple to manufacture and make it possible to achieve a high heating power.